Canadian patent 2,124,270 describes a method of finish machining external gear teeth where an internally threaded tool shaped like a ring gear with abrasive-faced internal teeth is meshed with an externally toothed workpiece and both the tool and workpiece are then rotated about their respective axes, which typically run skewly at a small acute angle to each other, for material removal from the tool. Before the actual machining operation a gauging of the workpiece is effected by meshing the tool and workpiece and relatively rotating them while monitoring their angular positions so as to determine which teeth need more or less material removal. Then during the actual machining operation the readings taken during the gauging step are utilized to relatively angularly position and drive the tool and workpiece to achieve the desired end shape.
The honing tools are, as mentioned, basically shaped as ring gears with internal abrasive-coated teeth. Such a tool has a fairly limited service life because the abrasive wears off. Although when the tool is fresh it is possible to produce the desired profile in the workpiece very quickly, when the tool is badly worn the process takes much longer.
Thus in order to ensure that the workpieces are all fully machined, it is standard to provide for a machining time that allows even a badly worn tool to be effective. Thus, for example, the machining time is set for 20 sec per workpiece, and the tool is replaced when it is starting to wear so that no bad workpieces are produced. This on the one hand lengthens overall machining time, and on the other hand does not fully use the tools.